The present invention relates generally to welding-type systems and, more particularly, to a system and method for coordinating delivery of a welding-type consumable using a multi-motor wire feeder system.
Typical wire feeders have a driven roller assembly for driving the consumable metal wire from a feed spindle through a welding gun for introduction to a weld. The drive mechanism in these driven roller assemblies typically includes a direct current (DC) motor or combination of DC motors. In a multi-motor drive configuration, a first motor is configured to take wire from the feed spindle and “push” it toward the gun. This motor is typically referred to as a “push motor.” Within this arrangement, a second motor is configured to “pull” the wire from the push motor and drive it to the weld. Accordingly, this motor is typically referred to as a “pull motor.”
Performance demands on wire feeders and torches not only require accurate speed but also accurate acceleration, deceleration, and braking control. That is, the consumable wire must be accurately controlled during the welding process and accurately disengaged from the welding-type process upon termination of the process. Failure to accurately control delivery of the consumable wire can result in excessive spatter, build-up on the tip of the wire, and generally provide less desirable welds.
In a multi-motor configuration, such as the aforementioned push-pull configuration, the operation of two separate motors must be satisfactorily coordinated to deliver the consumable wire to the weld. To control the push-pull configuration in certain prior art systems, the push motor is typically configured for constant torque operation and the pull motor is typically configured for constant speed operation. This control scheme delivers the consumable wire to the weld but can result in binding, birds nesting, and/or bunching of the consumable wire before or between the push motor and the pull motor.
For example, referring to FIG. 1, a known push-pull system is shown. A spool 1 is configured with a consumable wire 2 to be drawn by a push motor 3. The push motor 3 pushes the consumable wire 2 down a cable 4 to a pull motor 5. The pull motor 5 is constant speed controlled to pull the consumable wire 2 from the push motor 3 and deliver it to a torch tip 6. However, since the push motor 3 is configured for constant torque operation and the pull motor 5 is configured for speed operation, bunching, birds nesting, or binding 7 of the consumable wire 2 may occur within the cable 4 if the push motor 3 and pull motor 5 are even slightly unsynchronized. In particular, during startup or shutdown it is not uncommon for the push and pull motors to not be synchronized. In this case, the consumable wire 2 may become kinked or bent 8 when exiting the torch 6. These irregularities in the consumable wire 2 caused by bunching or binding 7 of the consumable wire 2 within the cable 5 can not only cause inaccurate welds but could also prevent welding all together. Additionally, imprecise wire feed is particularly troublesome in certain welding-type process, such as pulsed welding, where highly accurate control and delivery of the consumable wire 2 to the weld is required.
Many push-pull systems rely on fixed control schemes without feedback and, therefore, have no sensors, such as a tachometer, to monitor the wire 2. However, such fixed control schemes are “rigid” and are not readily adaptable to different torches that may include new or different pull motors. That is, the fixed control scheme is designed to accurately control specific push and pull motors. If the pull motor that the fixed control scheme is designed to control is removed, such as when replacing the gun 6, the fixed control scheme may not accurately control the new pull motor 5 associated with the new gun 6. Additionally, if a change is made in welding wire 2, such as gauge or type, the fixed control scheme may not be sufficiently flexible to maintain motor synchronization. Accordingly, separate fixed control schemes must be created for each combination of motors 3, 5, and wire, which is costly and time consuming.
Some systems include a tachometer 9 (shown in phantom) on the pull motor 5 to provide wire feed speed feedback at the pull motor 5 without regard to the push motor 3. In this case, the system is able to adapt control of the pull motor 5 based on feedback from the tachometer 9. However, since no feedback is received regarding the operation of the push motor 3, the push motor 3 may become unsynchronized with the pull motor 5, such as when changing welding wire 2 type or gauge, and cause bunching, birds nesting, or binding 7.
Yet other systems include tachometer sensors 9 (shown in phantom) on both the push and pull motors 3, 5 to keep the motors running at the same speed. While theses systems are able to adapt to changes in the motors, such as when switching guns 6 or welding wire 2, these systems require calibration to properly interpret the feedback from the tachometers 9 from the particular motors and synchronize the motor speeds. That is, these systems require re-synchronization whenever the gun 6 is changed and/or whenever there is a change in the type or size of wire 2.
Accordingly, it would be desirable to have a system and method for improved accuracy and control of welding-type consumable delivery that does not require regular re-synchronization/re-calibration. In particular, it would be desirable to have a technique to control the operation of a multi-motor wire feeder system to reduce bunching, binding, kinking, birds nesting, and/or bending of the consumable wire and provide a generally more accurate delivery of the consumable wire to the weld.